The present invention relates to radio frequency identification (RFID) technology, and more particularly to techniques that enable a device to advertise its mode of operation using an RFID tag attached to the device.
RFID tags are commonly used for inventory control and tracking of objects. It is well known that RFID chips are only readable from a few centimeters away, unless they are coupled to an antenna. However, once properly attached to an antenna, they are then visible from a much greater distance, for example, up to 10 meters in the case of RFID chips in the 2.4 GHz transmission band.
An RFID tag generally comprises a microchip coupled to an antenna. RFID tags are configured to respond to interrogation signals received from an RFID reader. The response signal transmitted from the RFID tag may then be read and used by the reader. An antenna attached to an RFID tag may be used for receiving an interrogation signal from an RFID reader and for transmitting signals in response to the interrogation signal.
Different types of RFID tags are available including active tags, passive tags, battery-assisted passive tags, and the like. An active RFID comprises a battery or other power supply that is used as a partial or complete source of power for the tag's microchip circuitry and antenna. Due to the presence of the battery, active tags can generally be read over longer distances than other tags. Active tags however tend to be physically larger and more expensive than passive tags.
A passive tag does not comprise an onboard power supply such as a battery. The power for a passive tag is supplied by the reader. A passive tag is activated by radio frequency (RF) energy in the interrogation signal transmitted from an RFID reader. A passive RFID tag generally comprises a coiled antenna that forms a magnetic field upon encountering radio waves from a reader. The passive RFID tag draws power from the magnetic coupling. The electrical current induced in the antenna by the incoming radio frequency signal provides enough power for a transponder in the tag to power up and transmit a response. Most passive tags transmit response signals by backscattering the carrier signal from the reader. The antenna in a passive tag may be designed to both collect power from the incoming signal and also to transmit the outbound backscatter signal. Since passive RFID tags do not require batteries, they are much smaller and less expensive than active tags and have a very long life span.
Although several applications presently make use of RFID tags, the ability to control the tags is still quite limited. Accordingly, better techniques are desired for controlling RFID tags that enable the RFID tags to be used for a whole new set of applications.